1. Field of the Invention
The present invention relates to a method and an apparatus for measuring roughness along the surface of a traffic area, e.g. a road or an airport runway.
More specifically, the invention concerns measuring the longitudinal dimension of the road, i.e. along a "wheel track", and not transverse to the road (for instance in order to measure the transverse profile of the wheel track).
2. State of the Prior Art
Previously known techniques for measuring roughness or evenness along a road track mainly comprise mechanical sensing techniques. During recent years optical techniques have also been put into use. For example, U.S. Pat. No. 4,653,316 discloses a vehicle comprising two attached laser devices longitudinally spaced in relation to each other, which devices emit light beams perpendicularly down towards the road surface. The light spots are read by corresponding detectors (focus detection).
U.S. Pat. No. 4,685,806 discloses a system in which stationary laser sources generate vertical and horizontal laser planes as a reference for a vehicle, which vehicle is equipped with "laser cameras" or the like, i.e. a transverse row of lasers/detectors or possibly ultrasound transducers directed down towards the road surface. A two-dimensional type mapping along the road track is thereby achieved, but the use of additional lasers for defining e.g. a horizontal plane is expensive and time-consuming.